Connect 120 volt circuits to get 240 volts

The inductive heating thing is silly; nothing would get measurably warm.

It's not really unsafe. The orthodox way to get 240V here is to use opposite 120V legs and a 2-pole breaker, so if one side trips, both sides open. But as long as you aren't in the habit of grabbing bare wires, it's fine to make 240 from two 120V sources.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

What happens if one of your two feed breakers trips (or is manually isolated) and you have a 240V load attached?

If your "dead" 120V circuit safe or not safe?

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Each wire is either 120 volts or zero volts either way.

Don't grab bare wires.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

I don't know about your code, but here, when a circuit is isolated, there is an expectation is it dead and at some point during electrical work, you have to touch wires.

Now a competent electrician would test the circuit, of course (!)

But let's suppose he did test circuit A, proved it dead and went to work on it. Mr C comes along with said 240V gizmo above and plugs it in (or plugs in the 240V load to a socket hack-wired likewise) such that the

240V is derived from:

Circuit A & Circuit B

Circuit B is live. Circuit A is now live, backfed via the load.

That is not a good situation.

The only safe way I can see is to either use a 120-240 transformer, or to correctly wire a 240V circuit according to code with double pole breakers.

This hacking stuff from random phase and antiphase circuits is an accident waiting to happen (not to mention if it is plugged in with no relays, or stuck relays, you have a potential "Jesus Cord" situation) :-0

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If you are afraid of electricity, better stay away from it.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

With the greatest of respect, this is not a good thing to promote on a public forum.

Me: I work with 240V competently and hold some qualifications under the British system (though my work is DIY - the qualification is to make the Building Inspector feel happy).

I have given you a scenario where a wrong side failure will put the life at risk, of a person who had nothing to do with, the hack being discussed.

I've also given a scneario where it puts the hacker's life at risk (or some poor fool who picks this device up and tries to use it)

If the only risk was to the idiot building this sort of device, then I'd have some sympathy that he's made his own decision.

But that's not the case and the more I look at this device, the less I like it and the more I will say so.

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Two 120V male plugs feeding one female socket that provides 240. Nothing hot exposed.

What is there to be afraid of? It's less dangerous than 240 to ground.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

You're free to take that attitude with your own life. But apply it to others and you [probably won't but] could end up on a very serious charge. Given your expertise I would not expect the legal system to have any sympathy.

NT

Inductive heating is science, not "silly". It is one of the reasons for the provisions in NEC article 300.

That might be true in his case, of course. But it also might NOT be true. That could be (pointlessly) debated, but the science holds true, whatever one says. As does the NEC, insofar as indicating that the wiring method his post indicates is incorrect.

Not sure what you have in mind with the word "really". Aside from worrying about that word, it's got two (at least) things against it being safe:

1) the possibility of inductive heating due to the wiring method 2) it violates the NEC

The part you wrote below is not relevant to the what I mentioned, nor to the discussion at all. But, since you mention it:

He has a single 240V source split into 2 phases, 180 degrees out of phase with each other. The right way to "make" 240 volts is to take it (already made) from the panel through the 2-pole breaker you mentioned and run proper wiring to the location where he needs the 240.

If he doesn't do that it is unsafe on the face of it, until and unless he posts details of his plan with approval of whatever his local "Authority Having Jurisdiction" (AHD) is. Generally speaking, that's the electrical inspector who performs the electrical plan review and rough in and final inspections.

Ed

If this hack is being used temporarily to get his car charged and nobody else is at the house/building AND he understands the risks that if he is the only one that is going to get hurt if something should happen and the system is not going to be inspected, then have at it.

But if the building should burn down because of this, he should be ready to NOT have insurance pay for any damage.

Interesting !

That sounds well and good, but a great many accidents have happened because a sloppy procedure had a blind eyed turned to them, until one day someone got caught out because something else happened that the person did not anticipate.

Indeed.

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I don't know if this was mentioned bur you will end up with a huge radiating loop once you connect the load.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

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Surely you *can* have it if you are prepared to pay (through the nose) for it?

240V 100A ought to be enough if you insulate the furnace properly.

That is under 2kW all up. You had better be living somewhere very friendly since there is no chance of powering an aircon on that.

A UK home typically has a 60A or 100A 240v mains supply. That is enough to run a glass furnace if you are so minded (and melt lead or aluminium). Though for both of those most people I know would use gas heating (only a handful of my friends cast metals at home).

My UK garage workshop has 240v 32A available (same as an electric cooker would). It is enough to run moderate sized power tools.

We don't much use aircon domestically since the climate is sufficiently temperate that the number of days when active cooling would be needed can be counted on the fingers of one hand. OTOH electric heating is sometimes used in the coldest months to top up oil or gas fired CH. Or in the summer months to make hot water when the CH is off.

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Regards, 
Martin Brown

But pointless. He is trying to get max. power out of it. Transformer can' t multiply power.

Yes, definitely. Even temporary hanging wires out of the main is better th an running wires from different rooms. Both are CODE VIOLATIONs anyway. M ost buildings save wires by wiring different phases to different rooms. Yo u would be lucky to find different phases to area close to each other.

What would be the failure mechanism that burns the building down?

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

The numbers are in the ballpark of 50 milligauss at 60 Hz. That's tiny.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Doesn't matter. Even if it's totally unrelated failure, insurance can denial claims.

OK, so there is no shock hazard, no fire hazard, no magnetic field problem, just emotional dislike and fear of electricity.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics